Abstract:

Disclosed herein are an apparatus and a technique for quickly detecting a
defective portion including wastage, which has occurred in piping having
a straight piping portion or a bending zone, in the nondestructive
inspection using a guided wave.
A guided wave sensor 3 included in a guided wave inspection device 4 is
mounted to the outer surface of piping 1. A guided wave is propagated to
an inspection area of the piping 1. If a defective portion exists, the
guided wave sensor 3 receives the guided wave that has been reflected
from the defective portion. As a result, the guided wave inspection
device 4 can acquire receive information including receive information
derived from the defect. On the other hand, receive information acquired
when piping, whose kind and shape are the same as those of the piping 1,
and which has no defect to be detected, is inspected by the guided wave
inspection device under the same conditions as those of the inspection of
the piping 1 is stored in an inspection result storage device 12 as
reference receive information. An inspection-result diagnostic device 13
compares the receive information acquired when the piping 1 to be
inspected has been inspected with the reference receive information,
which has been stored in the inspection result storage device 12, so that
significant receive information derived from the defect is extracted.

Claims:

1. A nondestructive inspection apparatus comprising:a guided wave
inspection device for propagating a guided wave into a piping, and for
receiving the guided wave from the piping to acquire receive information
based on the received guided wave;an inspection waveform storage device
for storing the receive information; andan inspection-result diagnostic
device for, on the basis of the receive information stored in the storage
device and predetermined reference receive information, performing
arithmetic processing of extracting receive information associated with a
defect that may occur in the piping.

2. The nondestructive inspection apparatus according to claim 1,wherein
said inspection waveform storage device stores the receive information
and estimated receive information which is estimated when a guided wave
propagating through the piping is received, the piping being free from a
defect to be detected, andwherein said inspection-result diagnostic
device performs arithmetic processing of extracting receive information
associated with a defect on the basis of the estimated receive
information and the receive information which are stored in the storage
device.

3. The nondestructive inspection apparatus according to claim 2,wherein
said inspection waveform storage device includes an operation processing
unit for calculating propagation behavior of a guided wave propagating
through the piping free from a defect to be detected to generate the
estimated receive information.

4. The nondestructive inspection apparatus according to claim 2,wherein
said inspection-result diagnostic device includes an operation processing
unit for calculating the difference in the receiving time between the
receive information and the reference receive information or between the
receive information and the estimated receive information, so as to
extract receive information associated with a defect.

5. A nondestructive inspection apparatus comprising:a pair of guided wave
inspection devices disposed on an outer surface of piping, each of
devices being capable of exciting an elastic wave into a piping to
propagate a guided wave, each of devices being capable of receiving the
guided wave propagating through the piping;an inspection-result storage
device for storing the guided wave received by said guided wave
inspection device as a digitized signal of the received wave;means for
transmitting, as a transmission signal, a waveform obtained by
time-reversing a waveform reproduced from said inspection-result storage
device from said pair of guided wave inspection devices; andan
inspection-result diagnostic device for, on the basis of a signal of each
received wave acquired by transmitting/receiving a guided wave based on
the time-reversed waveform into/from the piping by use of said pair of
guided wave inspection devices, performing arithmetic processing of
judging whether or not a signal associated with a defect exists.

6. A nondestructive inspection method comprising the steps of:disposing a
pair of means A and B, each of which is capable of generating and
receiving a guided wave, in such a manner that a range of piping to be
inspected is put between the pair of means A, B;receiving the guided wave
generated by one means A by the other means B, allowing the means B to
transmit the guided wave which has been subjected to waveform control by
time-reversing on the basis of the received wave to the range of piping
to be inspected, and handling a waveform received by the means B as a
received signal 1;receiving a guided wave generated by the means B by the
means A, allowing the means A to transmit the guided wave which has been
subjected to waveform control by time-reversing on the basis of the
received wave to the range of piping to be inspected, and handling a
waveform received by the means A as a received signal 2; andidentifying a
signal derived from a defect by calculating the sum and difference of the
receiving time between the received signal 1 and the received signal 2.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to a technical field in which the
nondestructive inspection is performed in piping including a pipe by use
of a guided wave so as to collectively evaluate, over long distance, a
defect such as wastage that is assumed to occur in a material.

[0003]2. Description of the Related Art

[0004]Piping used in a power plant, a chemical plant, or the like may be
subjected to corrosion and erosion on its inner surface due to influence
of liquid or gas flowing through the piping during the long-term
operation of the plant. As a result, deterioration of the piping is
promoted in some cases and what is worse, a hole may be disadvantageously
bored in piping in the thicknesswise direction thereof. In such a case,
fluid inside the piping such as liquid or vapor leaks and thereby normal
operation of the plant will not be performed. As a result, the plant is
obliged to stop the operation thereof for a long time. For this reason,
it is necessary to evaluate the thickness of piping and a state of
material using a nondestructive inspection technique, and then to take
measures including the replacement or repair of the piping before the
leakage occurs.

[0005]One of typical examples of the above-described nondestructive
inspection technique is a thickness measurement method using an
ultrasonic thickness gauge, which is specified in JIS Z 2355. The
thickness measurement method using the ultrasonic thickness gauge is a
method for measuring the thickness of piping by exciting an elastic wave
in a thickness direction of target piping using an ultrasonic probe, and
then by receiving the elastic wave reflected from the bottom surface of
the piping using the ultrasonic probe. This ultrasonic thickness gauge
measures the thickness of piping by use of the ultrasonic wave
propagation time based on a received wave and the known sound velocity
and is capable of measuring the thickness of piping with a high degree of
accuracy. However, an effective inspection range is a level of the piping
contact area of a probe. If a piping diameter is large, or if an
inspection range becomes wide (for example, piping whose length ranges
from several meters to several tens of meters), the number of measuring
points to be measured by the ultrasonic thickness gauge will increase. As
a result, it disadvantageously takes much time to complete the
inspection. In addition, in the case of such piping that it is difficult
for an inspector and an inspection apparatus to access the piping (for
example, piping covered by a heat insulator, buried piping, and vertical
piping which extends to a high place), it will take much time for the
preparation of inspection and clearance work after inspection.

[0006]To overcome the above-mentioned drawbacks, the inspection technology
using a guided wave, which can collectively inspect a long-distance wide
area, has being introduced. The principles of a guided wave will be
briefly described with reference to FIG. 1. A plurality of ultrasonic
sensors or magnetostrictive sensors are arrayed in the circumference
direction of piping 1. When the sensors are excited, a guided wave mode
is generated in which a guided wave propagates through a material in the
piping. Because guided waves have characteristics that the energy thereof
is not easily attenuated, the wave motion propagates over long distance.
In addition, when the exciting time is controlled, a wave motion mode
which allows a defect to be easily detected can be transmitted. If an
unevenness portion in thickness of piping is present in the propagation
direction (for example, if there is a wastage portion), a guided wave
propagating through a straight piping scatters a reflected wave towards
the upstream side of a transmitted wave. Thus, receiving the scattered
reflected wave makes it possible to detect a defect.

[0007]The conventional inspection method that uses a guided wave is
described in JP-A-2004-301540. According to this method, a guided wave
transmission technique is used to measure the depth of wastage of piping,
and the inspection result obtained is then displayed as an image for its
evaluation.

SUMMARY OF THE INVENTION

[0008]The nondestructive inspection method using a guided wave has an
advantage that because long-distance collective inspection can be
performed, inspection can be completed in a much shorter period of time
than that in the thickness measurement method that uses an ultrasonic
thickness gauge. Moreover, because the time it takes for the preparation
of inspection and clearance work after inspection can be shortened, it
becomes possible to shorten the total work hours including time for
preparation and removal processes.

[0009]However, the nondestructive inspection method using a guided wave
has an disadvantage that it is difficult to apply this inspection to a
bent portion of piping. Bending a portion of piping causes a piping
material to expand to some extent, resulting in uneven thickness. In
addition, at a bending zone, there is a difference in effective length of
piping between the inside and outside of the piping. Accordingly, when a
guided wave propagating through a straight piping portion passes through
the bending zone, piping deformation occurs, and part of a guided wave
breaks up and is reflected to be scattered and propagated toward the
upstream side of a transmitted wave. Because this makes it difficult to
detect a defect, the nondestructive inspection method using a guided wave
is not judged to be effective.

[0010]Therefore, when a bending zone of piping is to be inspected, the
thickness measurement using the ultrasonic thickness gauge described
above is obliged to be performed.

[0011]Therefore, an object of the present invention is to provide an
apparatus and a technique for quickly detecting a defect including
wastage, which has occurred in piping, in the nondestructive inspection
using a guided wave irrespective of whether a target to be inspected is a
bending zone or a straight piping portion.

[0012]In order to achieve the object of the present invention, in one
aspect, there is provided a nondestructive inspection apparatus
comprising: a guided wave inspection device for propagating a guided wave
into a piping, and for receiving the guided wave from the piping to
acquire receive information based on the received guided wave; an
inspection waveform storage device for storing the receive information;
and an inspection-result diagnostic device for, on the basis of the
receive information stored in the storage device and predetermined
reference receive information, performing arithmetic processing of
extracting receive information associated with a defect that may occur in
the piping.

[0013]Preferably, the inspection waveform storage device stores the
receive information and estimated receive information which is estimated
when a guided wave propagating through the piping is received, the piping
being free from a defect to be detected, and the inspection-result
diagnostic device performs arithmetic processing of extracting receive
information associated with a defect on the basis of the estimated
receive information and the receive information which are stored in the
storage device.

[0014]Preferably, the inspection waveform storage device includes an
operation processing unit for calculating propagation behavior of a
guided wave propagating through the piping free from a defect to be
detected to generate the estimated receive information.

[0015]Preferably, the inspection-result diagnostic device includes an
operation processing unit for calculating the difference in the receiving
time between the receive information and the reference receive
information or between the receive information and the estimated receive
information, so as to extract receive information associated with a
defect.

[0016]In another aspect, there is provided a nondestructive inspection
apparatus comprising: a pair of guided wave inspection devices disposed
on an outer surface of piping, each of devices being capable of exciting
an elastic wave into a piping to propagate a guided wave, each of devices
being capable of receiving the guided wave propagating through the
piping; an inspection-result storage device for storing the guided wave
received by the guided wave inspection device as a digitized signal of
the received wave; means for transmitting, as a transmission signal, a
waveform obtained by time-reversing a waveform reproduced from the
inspection-result storage device from the pair of guided wave inspection
devices; and an inspection-result diagnostic device for, on the basis of
a signal of each received wave acquired by transmitting/receiving a
guided wave based on the time-reversed waveform into/from the piping by
use of the pair of guided wave inspection devices, performing arithmetic
processing of judging whether or not a signal associated with a defect
exists.

[0017]In a still another aspect, there is provided a nondestructive
inspection method comprising the steps of: disposing a pair of means A
and B, each of which is capable of generating and receiving a guided
wave, in such a manner that a range of piping to be inspected is put
between the pair of means A, B; receiving the guided wave generated by
one means A by the other means B, allowing the means B to transmit the
guided wave which has been subjected to waveform control by
time-reversing on the basis of the received wave to the range of piping
to be inspected, and handling a waveform received by the means B as a
received signal 1; receiving a guided wave generated by the means B by
the means A, allowing the means A to transmit the guided wave which has
been subjected to waveform control by time-reversing on the basis of the
received wave to the range of piping to be inspected, and handling a
waveform received by the means A as a received signal 2; and identifying
a signal derived from a defect by calculating the sum and difference of
the receiving time between the received signal 1 and the received signal
2.

[0018]According to the present invention, it is possible to quickly detect
a defect by the inspection using a guided wave over a wide inspection
area including not only a straight piping portion of a piping but also a
bending zone whose thickness is obliged to be measured by the ultrasonic
thickness gauge.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is an overall view illustrating a nondestructive inspection
apparatus according to a first embodiment of the present invention;

[0020]FIG. 2 is a diagram illustrating a guided wave inspection method
that is generally used;

[0021]FIG. 3 shows charts each illustrating a defect identification method
using a nondestructive inspection apparatus according to the first
embodiment of the present invention;

[0022]FIG. 4 is a diagram illustrating a guided wave sensor according to
the first embodiment of the present invention;

[0023]FIG. 5 is an overall view illustrating a nondestructive inspection
apparatus according to a second embodiment of the present invention;

[0024]FIG. 6 is a diagram illustrating a first inspection process using a
nondestructive inspection apparatus according to the second embodiment of
the present invention;

[0025]FIG. 7 is a diagram illustrating a second inspection process using a
nondestructive inspection apparatus according to the second embodiment of
the present invention;

[0026]FIG. 8 is a diagram illustrating a third inspection process using a
nondestructive inspection apparatus according to the second embodiment of
the present invention;

[0027]FIG. 9 is a diagram illustrating a fourth inspection process using a
nondestructive inspection apparatus according to the second embodiment of
the present invention;

[0028]FIG. 10 shows charts each illustrating a fifth inspection process
using a nondestructive inspection apparatus according to the second
embodiment of the present invention;

[0029]FIG. 11 is a diagram illustrating an example 1 of a piping shape
that can be handled by the second embodiment of the present invention;

[0030]FIG. 12 is a diagram illustrating an example 2 of a piping shape
that can be handled by the second embodiment of the present invention;

[0031]FIG. 13 is a diagram illustrating an example 3 of a piping shape
that can be handled by the second embodiment of the present invention;

[0032]FIG. 14 is a diagram illustrating an example 4 of a piping shape
that can be handled by the second embodiment of the present invention;

[0033]FIG. 15 is a diagram illustrating an example 5 of a piping shape
that can be handled by the second embodiment of the present invention;

[0034]FIG. 16 is a flowchart illustrating the workflow according to the
second embodiment of the present invention;

[0035]FIG. 17 shows charts each illustrating a time-reversing wave
according to the second embodiment of the present invention; and

[0036]FIG. 18 is a diagram illustrating the time starting point adjustment
based on the difference in placement position between guided wave sensors
according to the second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037]Embodiments of the present invention will be described with
reference to drawings as below.

First Embodiment

[0038]A first embodiment of the present invention will be described with
reference to FIG. 1. A guided wave inspection device 4 is an device for
transmitting/receiving a guided wave into/from a piping. The guided wave
inspection device 4 includes a trigger signal generator 5, a plurality of
transmit-receive circuits 61 through 68, and a received waveform
converter 11 as main elements.

[0039]The transmit-receive circuit 61 is connected to an ultrasonic probe
21 through an electric wire 15. Here, the transmit-receive circuits 61
through 68 have the same configuration and function so that the
transmit-receive circuits 61 through 68 operate in the same manner. The
ultrasonic probes 21 through 28 have the same configuration and
performance so that the ultrasonic probes 21 through 28 operate in the
same manner.

[0040]Hereinafter, circuits relating to the transmit-receive circuit 61
and the ultrasonic probe 21 will be described. In addition, the
ultrasonic probes 21 through 28 are connected to the transmit-receive
circuits 61 through 68 respectively to have one-to-one correspondence.

[0041]A trigger signal transmitted from the trigger signal generator 5 is
transferred to the transmit-receive circuit 61. In response to this
trigger signal, a transmission signal is transmitted from an
arbitrary-waveform generator 7. An amplifier 8 amplifies the amplitude of
the transmission signal. The amplified transmission signal is then
transmitted to the ultrasonic probe 21.

[0042]The ultrasonic probe 21 receives the transmission signal. The
ultrasonic probe 21 then transmits an elastic wave into piping to induce
a guided wave in the piping so that the guided wave is propagated. If
there is unevenness such as wastage in the piping, a reflected wave
towards the upstream direction (propagation origin point) of the guided
wave, which is the transmitted wave, occurs. This reflected wave is
received by the ultrasonic probe 21.

[0043]The amplitude of the received signal is amplified by a receive
amplifier 9 of the transmit-receive circuit 61. The amplified signal is
then transmitted to a digital signal converter 10. The digital signal
converter 10 converts the amplified signal into a digital signal, and
then transmits the converted signal to a received waveform converter 11.
Next, the received waveform converter 11 performs superimposing
processing of signals obtained from the ultrasonic probes 21 through 28
so that the received signal is measured and identified as a received
waveform. The received signal and the received waveform subjected to the
superimposing processing are handled as receive information.

[0044]The received waveform converter 11, an inspection waveform storage
device 12, and a display unit 14 are connected to an inspection-result
diagnostic device 13. A received waveform acquired by measuring a region
to be inspected of piping using a guided wave sensor and the ultrasonic
probe is stored in the inspection waveform storage device 12 as reference
receive information. In this case, the region to be inspected of piping
is in a pre-service or molded based on the same process, material and
standards. Accordingly, the received waveform 31 stored beforehand can be
acquired from the inspection waveform storage device 12 when necessary.

[0045]As shown in FIG. 3, the inspection-result diagnostic device 13 has a
function of comparing a received waveform 31a stored beforehand by the
above means with a received waveform 32 acquired by the actual inspection
to determine a waveform 33 that is the difference between both of the
received waveforms. With the above function, if a significant signal 34
derived from a defect is detected, it is possible to judge that the
signal in question is based on the defect, and thereby defect detection
can be made. Waveforms shown in FIG. 3 are displayed on the display unit
14.

[0046]A guided wave sensor 3 will be described with reference to FIG. 4 as
below. The guided wave sensor 3 disposed on a straight piping portion of
the piping 1 is formed of halved guided wave sensor rings 3c, 3d, and a
plurality of ultrasonic probes 21 through 28. With the guided wave sensor
rings 3c, 3d joined together on the outside surface of the piping, the
guided wave sensor rings 3c, 3d are secured by use of guided wave sensor
fixtures 19 so that the guided wave sensor rings 3c, 3d are not displaced
from the piping.

[0047]The guided wave sensor rings 3c, 3d are provided for the guided wave
sensor 3 according to a piping diameter; basic configurations thereof are
the same. An elastic wave is transmitted into a material in the piping by
the ultrasonic probes 21 through 28 such that a signal derived from the
defect and the unevenness portion in the piping can be received.

[0048]In addition, one of the embodiments of the present invention is that
the inspection waveform storage device 12 has a function of calculating a
guided wave propagating through the piping. Here, when the guided wave
propagating through the piping is calculated, calculation grids are
automatically generated on the basis of information about a piping
diameter, the thickness, and a piping shape. After that, a numerical
analysis solution can be determined based on an analytical technique
represented by the finite element method in which material
characteristics and transmitted ultrasonic wave information are input
conditions. The numerical analysis solution is obtained by solving a
governing equation based on elastic theory. Thus, there is provided the
function of calculating propagation behavior of a guided wave propagating
through the piping. An estimated waveform 31b, which is a received
waveform acquired when the piping in question has no defect, is
calculated. The estimated waveform 31b is used as estimated receive
information.

[0049]The inspection-result diagnostic device 13 compares this estimated
waveform 31b with the waveform 32 that has been actually measured by the
guided wave inspection, and thereby calculates a waveform 33 that is the
difference between both of the waveforms. If a significant signal is
detected, it is possible to judge that the signal is based on the defect,
and thereby defect detection can be made. In addition, the estimated
received waveform 31b may also be stored in the inspection waveform
storage device 12 as a database.

[0050]This eliminates the need for acquiring the received waveform 31a
that is stored beforehand as a result of the guided wave inspection at
the time of the installation. Therefore, it becomes easy to apply the
guided wave inspection to the piping inspection of existing equipment.
Moreover, molding of new piping based on the same process, material, and
standards, and the preliminary inspection using the new piping, are
unnecessary.

Second Embodiment

[0051]A second embodiment of the present invention will be described with
reference to FIG. 5. Guided wave inspection devices 4a, 4b are devices
for transmitting/receiving a guided wave into/from a piping. The guided
wave inspection devices 4a, 4b have the same elements and functions, and
are capable of operating in the same manner.

[0052]The guided wave inspection device 4a includes a trigger signal
generator 5a, transmit-receive circuits 61a through 68a, and a received
waveform converter 11a. The transmit-receive circuit 61a is connected to
an ultrasonic probe 21a through an electric wire 15. Here, the
transmit-receive circuits 61a through 68a have the same configuration and
function so that the transmit-receive circuits 61a through 68a operate in
the same manner. The ultrasonic probes 21a through 28a have the same
configuration and performance, so that the ultrasonic probes 21a through
28a operate in the same manner.

[0053]Hereinafter, circuits relating to the transmit-receive circuit 61a
and the ultrasonic probe 21a will be described. In addition, the
ultrasonic probes 21a through 28a are connected to the transmit-receive
circuits 61a through 68a respectively to have one-to-one correspondence.

[0054]In addition, the guided wave inspection device 4b includes a trigger
signal generator 5b, transmit-receive circuits 61b through 68b, and a
received waveform converter 11b. The transmit-receive circuit 61b is
connected to an ultrasonic probe 21b through the electric wire 15. Here,
the transmit-receive circuits 61b through 68b have the same configuration
and functions so that the transmit-receive circuits 61b through 68b
operate in the same manner. The ultrasonic probes 21b through 28b have
the same configuration and performance, so that the ultrasonic probes 21b
through 28b operate in the same manner. Hereinafter, circuits relating to
the transmit-receive circuit 61b and the ultrasonic probe 21b will be
described. In addition, the ultrasonic probes 21b through 28b are
connected to the transmit-receive circuits 61b through 68b respectively
for one-to-one correspondence. A pair of means A, B, each of which is
capable of generating and receiving a guided wave, corresponds to the
guided wave inspection devices 4a, 4b respectively.

[0055]Guided wave sensors 3a, 3b are mounted on the outer surface of the
piping in such a manner that a region to be inspected is placed between
the guided wave sensors 3a, 3b. The guided wave sensors 3a, 3b are
configured in the same manner as that described with reference to FIG. 4.

[0056]A trigger signal transmitted from the trigger signal generator 5a is
transmitted to the transmit-receive circuit 61a. In response to this
trigger signal, a transmission signal is transmitted from an
arbitrary-waveform generator 7. An amplifier 8 amplifies the amplitude of
the transmission signal. The amplified transmission signal is then
transmitted to the ultrasonic probe 21a. The ultrasonic probe 21a
receives the transmission signal. The ultrasonic probe 21a then transmits
an elastic wave into piping to induce a guided wave in the piping. If
there is an unevenness portion (for example, wastage) in the piping, a
reflected wave towards an upstream direction of the transmitted wave
occurs.

[0057]This reflected wave is received by the ultrasonic probe 21. The
received signal is amplified by a receive amplifier 9 of the
transmit-receive circuit 61a and then the amplified signal is transmitted
to a digital signal converter 10. Next, the digital signal converter 10
converts the amplified signal into a digital signal. The digital signal
is then transmitted to a received waveform converter 11a in which the
digital signal is measured as a received waveform. The received waveform
converter 11, an inspection waveform storage device 12, and a display
unit 14 are connected to an inspection-result diagnostic device 13.

[0058]Inspection procedures according to the second embodiment will be
described with reference to FIGS. 6 through 10 and FIG. 16. To begin
with, processing in a step 101 shown in FIG. 16 is performed. As shown in
FIG. 6, in response to a trigger signal from the trigger signal generator
5a, transmitted waves each having the same waveform are transmitted from
the ultrasonic probe 21a through 28a according to the above-described
operation. In this case, the phase and excitation amplitude are adjusted
so that a guided wave mode which is suitable for inspection within a
target range is excited.

[0059]In this way, a guided wave free from breakup is transmitted into the
piping. When a guided wave propagates from a straight piping portion at
which the guided wave sensor 3a is disposed to a bending zone and then
passes through the bending zone, the guided wave is broken up at the
bending zone. This breakup is caused by: the unevenness in thickness
caused by the slight expansion that has occurred at the time of bending;
and the difference in effective length of piping between the inside and
outside of the bending zone. This broken-up guided wave is received by
the ultrasonic probes 21b through 28b of the guided wave sensor 3b. The
received signal is amplified by the receive amplifier 9 of each of the
transmit-receive circuits 61b through 68b and the amplified signal is
then transmitted to the digital signal converter 10. The digital signal
converter 10 converts the amplified signal into a digital signal, and
then transmits the digital signal to the received waveform converter 11b.

[0060]Next, processing in a step 102 shown in FIG. 16 is performed. As
shown in FIG. 17, the received waveform 37 acquired by the received
waveform converter 11b is transmitted to the arbitrary-waveform generator
7 as a waveform 38 whose signal is time-reversed so that a signal being
received late is transmitted first. In this case, the time-reversed
waveform in the ultrasonic probe 21b is adapted to be received into the
arbitrary-waveform generator 7 of the transmit-receive circuit 61b. The
arbitrary-waveform generators of the other transmit-receive circuits are
also set according to this configuration.

[0061]In addition, processing in a step 103 shown in FIG. 16 is performed.
As shown in FIG. 7, in response to a trigger signal from the trigger
signal generator 5b, a time-reversed wave, which has been inputted from
each of the ultrasonic probes 21b through 28b to the arbitrary-waveform
generator 7, is transmitted as an in-phase transmitted wave according to
the above-described operation.

[0062]When a wave having broken-up wave motion time-reversed is
transmitted, the wave passing through the bending zone becomes a wave
free from breakup, which is due to the reversibility of a wave motion.
This enables the wave motion control in the bending zone. Inspection is
carried out by use of this control transmission wave.

[0063]If a signal caused by bending or a defect such as wastage is present
in a region within a range to be inspected, a reflected wave is generated
from the region. The reflected wave is received by the ultrasonic probes
21b through 28b. The received signal passes through each of the
transmit-receive circuits 61b through 68b, and is then transmitted to the
received waveform converter 11b. The signal is subjected to the
arithmetic processing including waveform superimposing, and is then
recorded in the inspection result storage device 12 as a received
waveform 35.

[0064]Next, measurements are performed with transmission and receiving
functions switched between the guided wave sensors 3a, 3b. However, this
switching is electrically performed by a signal from the
inspection-result diagnostic device 13 to the trigger signal generator
5b. Processing in a step 104 shown in FIG. 16 is performed.

[0065]As shown in FIG. 8, in response to a trigger signal from the trigger
signal generator 5b, transmitted waves each having the same waveform are
transmitted from the ultrasonic probe 21b through 28b according to the
above-described operation. In this case, the phase and excitation
amplitude are adjusted so that a guided wave mode which is suitable for
inspection within a target range is excited. When a guided wave
propagates from a straight piping portion at which the guided wave sensor
3b is disposed to a bending zone, a guided wave is broken up and passes
through the bending zone.

[0066]This broken-up guided wave is received by each of the ultrasonic
probes 21a through 28a of the guided wave sensor 3a. The received signal
is then amplified by the receive amplifier 9 of each of the
transmit-receive circuits 61a through 68a and the amplified signal is
then transmitted to the digital signal converter 10. Next, the digital
signal converter 10 converts the amplified signal into a digital signal,
which is then transmitted to the received waveform converter 11a.

[0067]Next, processing in a step 105 shown in FIG. 16 is performed. The
received waveform acquired by the received waveform converter 11a is
transmitted to the arbitrary-waveform generator 7 as a waveform whose
signal is time-reversed so that a signal being received late is
transmitted first. In this case, the time-reversed waveform in the
ultrasonic probe 21a is adapted to be received into the
arbitrary-waveform generator 7 of the transmit-receive circuit 61a, and
based on this configuration, the arbitrary-waveform generators of the
other transmit-receive circuits are also set.

[0068]Then, processing in a step 106 shown in FIG. 16 is performed. As
shown in FIG. 9, in response to a trigger signal from the trigger signal
generator 5a, a time-reversed wave, which has been inputted from each of
the ultrasonic probes 21a through 28a to the arbitrary-waveform generator
7, is transmitted as an in-phase transmitted wave according to the
above-described operation. As illustrated in FIG. 7, this process enables
the broken-up-less wave control of a wave passing through the bending
zone.

[0069]Inspection is carried out by use of this control wave. If a signal
caused by bending or a defect such as wastage is present in a region
within a range to be inspected, a reflected wave occurring at this point
of time is received by the ultrasonic probes 21a through 28a. The
received signal passes through each of the transmit-receive circuits 61a
through 68a, and is then transmitted to the received waveform converter
11a. The signal is subjected to the arithmetic processing including
waveform superimposing, and is then recorded in the inspection result
storage device 12 as a received waveform 36.

[0070]Lastly, processing in a step 107 shown in FIG. 16 is performed. An
identification method for identifying a defect will be described with
reference to FIG. 10. The received waveform 35 received by the guided
wave sensor 3b and the received waveform 36 received by the guided wave
sensor 3a are output from the inspection result storage device 12 to the
inspection-result diagnostic device 13. After that, the inspection-result
diagnostic device 13 performs the undermentioned arithmetic operation.
The result of the arithmetic operation is output to the display unit 14.

[0071]In the embodiment of the present invention, a case where guided wave
sensors are disposed at positions, each of which is spaced away from the
central part of a bending zone by the same distance, will be described.
Incidentally, symbols shown in FIG. 10 are as follows: t11 and t21 denote
the back-and-forth propagation time of a signal caused by a bending
shape; t12 and t22 denote the back-and-forth propagation time of a signal
caused by a defect; and T denotes the back-and-forth propagation time of
a guided wave between the guided wave sensors 3A, 3B for a signal caused
by bending.

[0072]If it is assumed that a signal is caused by a bending shape, it is
judged that a bending zone has been symmetrically processed from the
central part. Accordingly, the signal appears at a position whose
distance from the guided wave sensor 3A is the same as that from the
guided wave sensor 3B. In other words, the signal appears at a position
at which the propagation time is the same. Therefore, equations 1 hold.
As a result, the signal can be extracted as a nondefective signal.

t11=t21, t11+t21≠T (Equation 1)

[0073]Therefore, on the basis of the equations 1, it is possible to
determine a waveform 37 that is the difference between the received
waveform 35 and the received waveform 36. Next, if it is assumed that the
signal is caused by a defect, the sum of the distance from a defective
portion to the guided wave sensor 3A and the distance from the defective
portion to the guided wave sensor 3B is equivalent to the distance
between the guided wave sensors 3A and 3B. Accordingly, the sum of the
receiving time is calculated for all combinations of signal components
that exceed a predetermined threshold value of the amplitude of the
waveform 37. A signal which satisfies the relationship of an equation 2
can be identified as a defect.

t12+t22=T (Equation 2)

[0074]However, a signal generated from the central part of the bending
zone satisfies the equation 2 even if the signal is caused by a bending
shape. In this case, inspection is performed by use of a guided wave
whose transmit frequency has been changed, or a guided wave whose phase
and excitation amplitude has been adjusted. Then, a signal is reevaluated
according to the steps described with reference to FIGS. 6 through 10.
Here, if a significant signal satisfying the equation 2 is obtained, it
is desirable to evaluate the soundness by auxiliary means such as
thickness measurement using an ultrasonic thickness gauge.

[0075]In the embodiment of the present invention, a case where both of the
guided wave sensors are disposed at positions, each of which is spaced
away from the central part of the bending zone by the same distance, was
described. However, even if both of the guided wave sensors are disposed
at positions, each of which is spaced away from the central part of the
bending zone by the different distance, if a time starting point is
shifted according to the distance, it is possible to carry out the defect
identification according to the present invention. Therefore, this case
also falls within the category of the present invention. For example, as
shown in FIG. 18, on the assumptions that the distance from the center of
the bending zone to the center of the guided wave sensor 3a is La, and
that the distance from the center of the bending zone to the center of
the guided wave sensor 3b is Lb, and that the sound velocity of a guided
wave propagating through the piping is V, the moving time T of a time
starting point is expressed by an equation 3. If the guided wave sensors
are placed at positions shown in FIG. 18, the processing described in
FIG. 10 becomes effective by subtracting only T from the receiving time
of a received waveform of the guided wave sensor 3b.

T=(Lb-La)/V (Equation 3)

[0076]Although the steps using the time reversing was described as above,
there is a case where a waveform is not broken-up depending on the
transmit frequency and a bending shape, and therefore, it is not
necessary to use the waveform control based on the time reversing. In
this case, because it is not necessary to use the waveform control based
on a time-reversing wave, the processing relating to the generation of
the time-reversing wave can also be excluded.

[0077]In addition, according to the embodiment of the present invention,
the diagram illustrating the curved piping whose bending angle is
90° was made. However, even in a straight piping, a bending zone
as shown in FIGS. 11 through 13, a T-shaped branch piping as shown in
FIG. 14, and piping equipped with a support structure 38 as shown in FIG.
15, piping inspection of piping whose range to be inspected includes a
symmetrical shape also fall within the category of the present invention.

[0078]As described in the embodiment of the present invention, according
to the defect identification method in which two received signals are
compared in the inspection using a guided wave so as to identify a defect
from the significant difference that exceeds a predetermined threshold
value of the amplitude, it is possible to detect a defect by the
inspection using a guided wave even in a bending zone whose thickness is
obliged to be measured by an ultrasonic thickness gauge. This makes it
possible to complete the inspection in a shorter period of time than that
in the thickness measurement using the conventional ultrasonic thickness
gauge. In particular, in a case where a caliber is large, a guided wave
sensor suitable for the large caliber may be selected so that the
inspection by the totally same system is possible. Therefore, the effects
of reducing the inspection time are very large in comparison with the
method using the ultrasonic thickness gauge which has enormous number of
thickness measuring points.

[0079]As described in each of the above embodiments, the description
includes a number of technical points, which will be described as below.
To be more specific, a first technical point relates to a nondestructive
inspection apparatus including: generation means for exciting an elastic
wave into a piping to propagate a guided wave, the generation means being
disposed on an outer surface of the piping; receiving means for receiving
the guided wave propagating through the piping, the receiving means being
disposed on the outer surface of the piping; recording means for
converting the guided wave received by the receiving means into a digital
signal so that the digital signal is handled as a received wave; storage
means for storing the received wave that has been acquired by the
recording means; and diagnosis means that is capable of carrying out
arithmetic processing for the signal obtained by reproducing the received
wave which has been stored in the storage means, and for a signal of the
received wave which has been recorded by the recording means.

[0080]A second technical point relates to a nondestructive inspection
apparatus including: generation means for exciting an elastic wave into a
piping to propagate a guided wave, the generation means being disposed on
an outer surface of the piping; receiving means for receiving the guided
wave propagating through the piping, the receiving means being disposed
on the outer surface of the piping; recording means for converting the
guided wave received by the receiving means into a digital signal so that
the digital signal is handled as a received wave; calculation means for
calculating the behavior of the guided wave propagating through the
piping on the basis of characteristics of the piping and information
about a transmission signal of propagation means; storage means for
storing a calculated waveform that has been acquired by the calculation
means; and diagnosis means that is capable of carrying out arithmetic
processing for the signal obtained by reproducing the calculated waveform
which has been stored in the storage means, and for a signal of the
received wave which has been recorded by the recording means.

[0081]A third technical point relates to the nondestructive inspection
apparatus according to the first or second technical point, wherein: on
the basis of the difference in receiving time between a read signal and a
received signal, it is possible to detect a defect that has occurred in
the piping.

[0082]A fourth technical point relates to a nondestructive inspection
apparatus including: a pair of means that is capable of exciting an
elastic wave into a piping to propagate a guided wave, and that is
capable of receiving the guided wave propagating through the piping, the
pair of means being disposed on an outer surface of the piping; recording
means for converting the guided wave received by the receiving means into
a digital signal so that the digital signal is handled as a received
wave; storage means for storing the received wave that has been acquired
by the recording means; and means for transmitting, from the pair of
means, a waveform as a transmission signal, the waveform being obtained
by time-reversing a waveform reproduced from the storage means; and
diagnosis means that is capable of carrying out arithmetic processing for
the signal obtained by reproducing the received wave which has been
stored in the storage means, and for a signal of the received wave which
has been recorded by the recording means.

[0083]A fifth technical point relates to a nondestructive inspection
method including the steps of: disposing a pair of means A, B, each of
which is capable of generating and receiving a guided wave, in such a
manner that a range of piping to be inspected is put between the pair of
means A, B; receiving the guided wave, which has been generated by the
one means A, by the other means B, and transmitting the guided wave,
which has been subjected to the waveform control by time-reversing on the
basis of the received wave, to the range of piping to be inspected by the
means B, and then handling a waveform received by the means B as a
received signal 1; receiving, by the means A, the guided wave that has
been generated by the means B, and transmitting the guided wave, which
has been subjected to the waveform control by time-reversing on the basis
of the received wave, to the range of piping to be inspected by the means
A, and then handling a waveform received by the means A as a received
signal 2; and identifying a signal caused by a defect by calculating the
sum and difference of the receiving time between the received signal 1
and the received signal 2.

[0084]Any of the above-described technical points makes it possible to
detect, by the inspection using a guided wave, a defect in a bending zone
whose thickness is obliged to be measured by an ultrasonic thickness
gauge. As a result, it becomes possible to complete the inspection in a
shorter period of time than that in the thickness measurement using the
conventional ultrasonic thickness gauge. In particular, in a case where a
caliber is large, a guided wave sensor suitable for the large caliber may
be selected so that the inspection by the totally same system is
possible. Therefore, the effects of reducing the inspection time are very
large in comparison with the method using the ultrasonic thickness gauge
which has enormous number of thickness measuring points.

[0085]The present invention is applicable to the nondestructive inspection
that uses a guided wave to inspect whether or not piping has a defect
including wastage.